Runway sheave assembly for aircraft-arresting gear

ABSTRACT

The runway sheaves of an aircraft-arresting gear are mounted at the bottom of a hinged cover assembly and received within a pit prior to activation. The linear payout element is deflected into a deep bend under the closed cover assembly by a knee element. The cover assembly is locked down by shear pins. The strong tensioning of the linear payout element during the initial phase of arrestment breaks the shear pins and raises the cover assembly. The cover assembly is then latched in a raised position to maintain the sheave and payout element elevated above ground level and facilitate their action during arrestment of the aircraft. Fairleads and slots smoothly guide the linear payout element under and through the cover assembly, which is efficiently fabricated from a cover plate and a lower plate disposed at an acute angle beneath it. The sheaves are mounted between an inner plate spaced above and parallel to the lower plate and the knee element extends downwardly from the edge of the inner plate remote from the hinge. The cover assembly is of truncated V-shape in plan with its narrow end adjacent the runway and a hinge at its wider opposite end. The cover and inner plates are spaced apart by angular channels disposed parallel to the sides of the assembly and a slotted cross channel is secured between the inner and lower plates. A striker bar for the latch is conveniently made from the extended web of a lateral channel mounted beneath the narrower end of the assemblies. The latches and shear pin retainers are mounted on catch plates secured to the pit adjacent the narrow end of the cover assembly.

United States Patent [72] Inventor Barry C. Rlblett, Jr.

Wilmington, Del. [21] Appl. No. 20,004 [22] Filed Mar. 16; 1970 [45]Patented Nov. 16, 1971 [73] Assignee All American Industries, Inc.

Wilmington, Del.

[54] RUNWAY SHEAVE ASSEMBLY FOR AIRCRAFT- ARRESTING GEAR 24 Claims, 9Drawing Figs.

[52] U.S.Cl 244/110C l [50] Field of Search ..244/1 10, 63

[56] References Cited UNITED STATES PATENTS 3,182,935 5/1965 Wischhoefer244/110 A FOREIGN PATENTS 916,588 l/l963 Great Britain 244/110 PrimaryExaminer-Milton Buchler Assistant E.raminer Paul E. SaubererAllorney-Connolly and Hutz ABSTRACT: The runway sheaves of anaircraft-arresting gear are mounted at the bottom of a hinged coverassembly and received within a pit prior to activation. The linearpayout element is deflected into a deep bend under the closed coverassembly by a knee element. The cover assembly is locked down by shearpins. The strong tensioning of the linear payout element during theinitial phase of arrestment breaks the shear pins and raises the coverassembly. The cover assembly is then latched in a raised position tomaintain the sheave and payout element elevated above ground level andfacilitate their action during arrestment of the aircraft. Fairleads andslots smoothly guide the linear payout element under and through thecover assembly, which is efficiently fabricated from a cover plate and alower plate disposed at an acute angle beneath it. The sheaves aremounted between an inner plate spaced above and parallel to the lowerplate and the knee element extends downwardly from the edge of the innerplate remote from the hinge. The cover assembly is of truncated V-shapein plan with its narrow end adjacent the runway and a hinge at its wideropposite end. The cover and inner plates are spaced apart by angularchannels disposed parallel to the sides of the assembly and a slottedcross channel is secured between the inner and lower plates. A strikerbar for the latch is conveniently made from the extended web of alateral channel mounted beneath the narrower end of the assemblies. Thelatches and shear pin retainers are mounted on catch plates secured tothe pit ad- 7 jacent the narrow end of the cover assembly.

PATENTEDunv 1s l97| 3,620,489

' sum 1 or 4 RUNWAY SHEAVE ASSEMBLY FOR AIRCRAFT ARIRESTING GEARBACKGROUND OF THE INVENTION This invention relates to a pit-mountedrunway sheave assembly for an aircraft arresting gear and it moreparticularly relates to an automatically raised device. Sheaveassemblies are mounted alongside airport runway to guide and restrainthe linear payout element of aircraft-arresting gear during anarrestment. Intermediate cross runway elements are bidirectional andrequire a pair of sheaves, whereas terminal runway units areunidirectional and only require a single sheave. Since the sheaves aremounted close to or on the edge of the runway, they must not create anabove-ground obstruction in the path of aircraft or personnel. U.S. Pat.No. 3,] 82,935 shows an arrangement for holding a runway sheave assemblydown in a depression until the aircraft-arresting gear is actuated. Itutilizes a lifting motor, thus complicating the device and its controland making it subject to malfunction.

An object of this invention is to provide a pit-mounted runway sheaveassembly which is simple, rugged and dependable In operation.

SUMMARY The sheave or pair of sheaves are mounted beneath a hinged coverassembly disposed within a pit prior to activation. The linear payoutelement is deflected into a deep bend under the cover assembly by a kneeelement in line with the sheave. The cover assembly is releasably lockedin a closed position to permit the payout element to be pretensioned apredetermined amount without raising the cover assembly. Thesubstantially deep bend creates an upwardly directed component of forcein response to tensioning of the payout element, which is sufficientduring the initial phase of arrestment to exceed the predeterminedupward force for releasing the lock. This quickly elevates the coverassembly in response to the resultantly strong tensioning of the payoutelement. A latch holds the cover assembly and its sheave and payoutelement elevated above ground level during arrestment of the aircraft tofacilitate their action. The payout element on both sides of the sheaveassembly may be disposed above ground level and fairleads and suitableslots are provided for smoothly guiding the payout element under andthrough the cover assembly.

The cover assembly is efficiently fabricated from a cover plate and alower plate disposed at an acute angle below it and which are connectedadjacent the hinge. The sheave is mounted between an inner plate spacedabove and parallel to the lower plate, and the knee element extendsdownwardly from the edge of the inner plate remote from the hinge. Anadvantageous form of cover assembly is a truncated V-shape in plan withits narrow end adjacent the runway and its hinge at the wider oppositeend. The cover and inner plates are spaced apart by angular channelsdisposed parallel to the sides of the assembly, and a slotted crosschannel is secured between the inner and lower plates. A striker bar forthe latch is conveniently comprised of the extended web ofa lateralchannel mounted beneath the narrower end of the cover assembly, whichengages the latches on catch plates secured to the walls of the pit.These catch plates may also include shear pin retainers for locking thecover assembly down in the closed position.

BRIEF DESCRIPTION OF THE DRAWING Novel features and advantages of thepresent invention will become apparent to one skilled in the art from areading of the following description in conjunction with theaccompanying drawing wherein similar reference characters refer tosimilar FIG. 3 is a plan view partially broken away of the embodimentshown in FIGS. 1 and 2;

FIG. 4 is a cross-sectional view taken through FIG. 3 along the line4-4;

FIG. 5 is a cross-sectional view in elevation of the embodiment shown inFIGS. 1, 3 and 4 in the raised position;

FIG. 6 is a cross-sectional view taken through FIG. 5 along the line6-6;

FIG. 7 is a cross-sectional view taken through FIG. 5 along the line7-7;

FIG. 8 is a cross-sectional view of another embodiment of this inventionin the raised activated position; and

FIG. 9 is a cross-sectional view in elevation of the embodiment shown inFIG. 8 in the closed lowered position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 is shown a pair ofpit-mounted runway sheave assemblies 10 for an aircraft-arresting gear12 having a linear payout element 14 connecting a cross runway element16 with energy absorber 18. Cross runway pendant I6 is, for example,steel cable or a nylon rope as described in US. Pat. No. 3,456,908.Linear payout element 14 is, for example, nylon tape or steel cable asdescribed in US. Pat. No. 3,467,347. Energy absorber I8 is, for example,of the type described in US. Pat. No. 3,172,625, which also describes anylon tape suitable for use as linear payout element [4. Tape I4 isconnected to cross runway pendant 16 by connector 20.

Hook 22 on aircraft 24 engages pendant 16 during the arrestment shown inFIG. 1. Hook 22 is, for example, of the type shown in US. Pat. No.2,989,272. This arrestment raises sheave assembly 10 from the closedlower position shown in FIG. 2 to the raised position shown in FIG. 1 aslater described in detail.

FIGS. 3 and 4 show sheave assembly 10 in the lowered position in whichthe portions of tape 14 at the entrance end 26 and exit end 28 aredisposed flat to the ground in contact with entrance fair-lead 30 andexit fair-lead 32 mounted at the corresponding edges of pit 34 throughslots 108 and 110. The sheave assembly is mainly comprised of a coverassembly 36 which is a truncated V-shape in plan with its narrower end38 disposed adjacent the runway and its wider end 40 oppositely disposedand rotatably connected to the corresponding entrance wall 42 of pit 34by hinge 44 secured to wall 42 by anchoring beam 46. Hinge 44 includes apair of hinge arms 48 connected to the wider end 40 of cover assembly36.

Cover assembly 36 includes a cover plate 50 and an angularly disposedlower plate 52. An inner plate 54 is spaced below cover plate 50 by apair of angular channels 56 disposed substantially parallel to the sidesof the narrow end 38 of cover plate 50 as shown in FIG. 3. Inner plate54 is spaced parallel and above lower plate 52 by slotted cross channel58 having a central slot 60 to provide a path for tape I4. A pair ofsheaves 62 are rotatably mounted between inner plate 54 and lower plate52 and tape 14 passes between them thus making sheave assembly 10bidirectional in action. As shown in FIGS. 3 and 4, the portion of tape14 between entrance section 26 and sheaves 62 is twisted approximately Aknee element 64 is mounted below cover assembly 36 remote from hinge 44.Tape 14 is thus deflected in a deep bend within pit 34 as shown in FIG.4. The portion of tape 14 between sheaves 62 and knee 64 is twisted inan additional 90 to make tape 14 twist approximately from entrancefairlead 30 to knee 64 and exit fair-lead 32.

Striker channel 66 is mounted under the end of lower plate 52 remotefrom hinge 44. It includes web extensions 68 shown in FIG. 7 whichengage latches 70 secured to catch plates 72 mounted at the narrow endof pit 34 and connected to frame 74 about the perimeter of pit 34. Theaction of latches 70 is later described in detail in conjunction withFIGS. 5 and 6. A pair of releasable locks provided by shear pinassemblies 76 connects the narrow end 38 of cover plate 50 to catchplates 72 to releasably lock it in a closed position. This permits tape14 to be pretensioned a predetermined amount without raising coverassembly 10. Shearable assemblies 76 include shear pin retainers 78,catch plates 72 and shear pins 80 which engage over the narrow end ofcover plate 50. The rewind motor 82 in energyabsorber I8 is actuated topretension tape 14, for example, about l,500 lbs. to hold cross runwaypendant 16 straight across runway 84 in position for engaging landingaircraft 24. Shear pins 80 are designed to hold cover assembly 36 in theclosed position against this pretensioning load.

FIGS. -7 show the condition of sheave assembly in the raised position ofFIG. 1. The substantially deep bend of tape 14 shown in FIG. 4 belowcover assembly 36 creates an upwardly directed component of force alongtape section 86 between knee 64 and exit fair-lead 32. This upwardlydirected component of force designated by arrow 88 is sufficient duringthe initial phase of arrestment shown in FIG. 1 to exceed the breakingstrength of shear pins 80 and thus raise cover assembly 36 in responseto the resultantly strong tensioning of tape 14 by the initial shock ofengagement of aircraft 24 with pendant 16. This strong shock forciblyrotates cover assembly 36 upwardly from pedestal 89 at the bottom of pit34 into the raised position shown in FIGS. 5-7. Web extensions 68 ofstriker channel 66 engage latch 70 to hold cover assembly 36 in theraised position. This positions sheaves 62 above the ground to allowtape 14 to untwist and assume the substantial vertical untwistedcondition shown in FIGS. 1, 5 and 6 to facilitate its smooth arrestingaction. The upward movement of web extension 68 is smoothly buffed byresilient pads 90 beneath catch plates 72.

Additional structural features of sheave assembly 10 include frame 74within which cover plate 50 nests in the lowered position shown in FIGS.2-4 to allow it to smoothly traverse aircraft wheels over it. Innerplate 54 also includes a pair of lateral extensions 92 secured under thehinged portion of cover plate 50. FIG. 6 shows vertical slot 94 in knee64. It provides apath for tape 24 when cover assembly 36 is in theraised position shown in FIGS. 5 and 6.

FIGS. 8 and 9 show runway sheave assembly 10A which is adapted for usewith a cross runway net 16A instead of cross runway pendant 16X. Theaxis of rotation 96A ofsheaves 62A is thus inclined at an oblique angleto the ground 98A to incline tape 14A for direct connection to the endof net 16A. A restraining and deflecting roller 100A is mounted betweenroller 96A and energy absorber 18A to prevent tape 14A from being liftedabove the line of action of sheave 62A during arrestment. Only onesheave 62A is provided because nets, such as 16A, arenormally mounted atthe terminal ends of the runway and only unidirectional action need beprovided.

Another feature of runway sheave assembly 62A and its associated net 16Aand energy absorber 18A is their complete underground installation.Energy absorber 18A is mounted in pit l02A and with a substantialhorizontal axis of rotation to provide an untwisted section 104A of tape14A from energy absorber 18A to horizontal roller 100A. Horizontalroller 100A cooperates with entrance fair-lead 30A to confine tape 14Abetween them.

As shown in FIG. 9, tape 14A from knee 64A is guided through coveredtrough 103A over entrance fair-lead 32A to net 16A which is stored inthe unactivated condition within a cross runway trough 106A. A netinstallation of such type is, for example, described in US. Pat. No.3,058,703. The entire installation is thus maintained below ground leveland out of the path of personnel and aircraft prior to activation. Thisbelow ground installation is shown in conjunction with a terminal runwaysystem, but is even more advantageous in an intermediate runwayposition, which is more subject to aircraft and personnel groundtraffic. The canted position of sheave 62A shown in FIG. 8 provides adirect efficient line of action therebetween and prevents rubbing of theedge of 14A on flanges (not shown) which might be provided on sheave62A. Such edge rubbing has been the source of extensive friction andwear.

OPERATION Prior to actuation, sheave assembly 10 is in the loweredclosed position shown in FIG..2. The pretensioning of tape 14 causesportion 26 entering sheave assembly 10 and portion 28 leaving sheaveassembly 10 to lie flat against the ground. This maintains cover plate50 and runway pendant 16 in firm smooth contact with the ground toprevent them from interfering with personnel and aircraft trafiic.

Landing aircraft 24 shown in FIG. 1 engages pendant 16 by hook 22 andexerts a strong tensioning force on pendant l6 and connected tape 14.The locking action of shear pins first prevents cover assembly 36 fromrising and holds it in a lowered position shown in FIGS. 2-4, until thebreaking strength of shear pins 80 is exceeded. Then, a strong componentof force illustrated by arrow 88 in FIG. 4 reacts upwardly against knee64 which snaps cover assembly 36 up to the raised position shown inFIGS. 5 and 6. Tape 14 untwists from the 180 bend of the loweredposition in FIGS. 2-4 to assume the vertical untwisted position ofFIGS. 1. 5 and 6. Slot 94 in the center of knee 64 provides an unimpededpath for tape 14 in the activated position.

Bumper pads smoothly arrest the upward movement of cover assembly 36 bystopping the upward movement of web extensions 68 on striker channel 66.Webs 68 also engage over latches 70 to hold cover assembly 36 in theraised position during arrestment and rewind.

After rewind, latches 70 are released to drop cover assemblies 36 backinto pit 34 and onto pedestal 89. Cover plate 50 then nests within frame74 to smoothly align itself with the ground. Tape 14 reassumes thetwisted condition shown in FIGS. 2-4 and passes through cover plate 50through entrance slot 108 and exit slot 110 in flat contact withentrance fairlead 30 and exit fair-lead 32. Slot 60 in cross channel 58provides the path for tape 14 to sheaves 62. Tape 14 passes under knee64 before engaging exit fair-lead 32.

The action of sheave assembly 10A in FIGS. 8-9 is similar to thatpreviously described with the exception of the use of single sheave 62A,the connection to net [6A, the advantageous inclination of sheave 62Aand the complete below-ground installation of the system. Also as shownin FIGS. 8 and 9, no twist ever occurs in the portion 104A of tape 14Abetween energy absorber 18A and opposed deflecting roller A andfair-lead 30A.

I claim:

1. A pit-mounted runway sheave assembly for an aircraft arresting gearhaving a linear payout element connecting a cross runway element with anenergy absorber comprising a cover assembly, horizontal hinge meansconnecting said cover assembly to a side of said pit to provide raisingand closing movement thereof, a knee element mounted beneath said coverassembly remote from said hinge means and extending downwardly below it,rotatable sheave means mounted beneath said cover assembly between saidknee element and said hinge means, said knee element being long enoughto indent said linear payout element downwardly into a substantiallydeep bend into said pit, locking means which is releasable at apredetermined upward force securing said cover assembly to a wall ofsaid pit when said cover assembly is down in the closed position wherebysaid linear payout element may be pretensioned a predetermined amountwithout raising said cover assembly, said substantially deep bendcreating an upwardly directed component of force in response totensioning of said payout element which is sufficient during the initialphase of arrestment to exceed said predetermined upward force forreleasing said locking means whereby said cover assembly is allowed torise in response to the resultantly strong tensioning of said payoutelement and latching means reacting between said cover assembly and awall of said pit for holding said cover assembly in said raised positionwhereby said sheave means and said payout element are elevated aboveground level during said arrestment to facilitate their action.

2. A runway sheave assembly as set forth in claim 1, wherein said linearpayout element connected to each end of said runway sheave assembly isdisposed above ground level, and fairleads are disposed at the entranceand exit edges of said pit whereby said linear payout element issmoothly guided into and out of said pit.

3. A runway sheave assembly as set forth in claim 1, wherein said coverassembly comprises a cover plate and a lower plate disposed at an acuteangle relative to each other and connected adjacent said hinge means, aninner plate disposed between said cover and lower plates andsubstantially parallel and spaced from said lower plate, said sheavemeans being rotatably mounted between said inner and said lower plates,and said knee element extending downwardly from the edge of said innerplate remote from said hinge means.

4. A runway sheave assembly as set forth in claim 3, wherein the loweredge of said knee element is centrally slotted to receive said linearpayout element.

5. A runway sheave assembly as set forth in claim 4, wherein said linearpayout element comprises a linear tape disposed in contact with thelower edge of said knee element and the side of said sheave, said loweredge of said knee element being substantially horizontally disposed, andthe side of said sheave means being substantially vertically disposedwhereby said tape is twisted about 90' between said sheave means andsaid knee element.

6. A runway sheave assembly as set forth in claim 5, wherein said tapeon both sides of said sheave assembly is disposed above the ground,entrance and exit fairleads are disposed at the entrance and exit edgesof said pit for smoothly guiding said above ground portion of said tapewhich are substantially flat with said ground when said cover assemblyis in the lowered position, and said tape being twisted through anadditional 90 between said sheave means and said entrance fairlead.

7. A runway sheave assembly as set forth in claim 1, wherein said sheavemeans comprises a pair of sheaves and said linear payout element isdisposed between said pair of sheaves to make said sheave assemblybidirectional in action.

8. A runway sheave assembly as set forth in claim 1, wherein saidlocking means comprises shearable means.

9. A runway sheave assembly as set forth in claim 1, wherein saidlatching means comprises a resilient latch mounted on said wall of saidpit and a striker bar mounted upon a lower portion of said coverassembly for engaging said resilient latch.

10. A runway sheave assembly as set forth in claim 2, wherein slots areprovided through said cover assembly adjacent said entrance and exitedges of said pit to provide a path for said linear payout element tosaid sheave means and said knee element.

11. A runway sheave assembly as set forth in claim 1, wherein a pedestalis provided in said pit to help support said cover assembly within saidpit in said lowered position.

12. A runway sheave assembly as set forth in claim 3, whereinintermediate angular brace is disposed between said cover and said innerplate and a slotted cross brace is disposed between said inner and saidlower plates.

13. A runway sheave assembly as set forth in claim 12, wherein saidinner plate includes a pair of lateral extensions connected below saidcover plate.

14. A runway sheave assembly as set forth in claim 1, wherein said coverassembly is substantially a truncated V- shape in plan having itsnarrower end disposed adjacent said runway and said hinge means disposedat its wider end.

15. A runway sheave assembly as set forth in claim 14, wherein saidcover assembly comprises a cover plate and a lower lates, and said kneeelement extending downwardly from t e edge of said inner plate remotefrom said hinge means.

16. A runway sheave assembly as set forth in claim 15, wherein a pair ofangular channel braces are mounted between said cover and said innerplates and substantially parallel to the sides of said truncatedV-shaped cover assembly.

17. A runway sheave assembly as set forth in claim 16, wherein a crossbrace comprising a centrally slotted channel is laterally securedbetween said inner and said lower plates, and said central slotproviding a path for said linear payout element through said coverassembly.

18. A runway sheave assembly as set forth in claim 17. wherein the loweredge of said knee element is slotted to provide a path for said linearpayout element.

19. A runway sheave assembly as set forth in claim 18, wherein said tapeon both sides of said sheave assembly is disposed above the ground,entrance and exit fairleads are disposed at the entrance and exit edgesof said pit for smoothly guiding said above-ground portions of said tapewhich are substantially flat with said ground when said cover assemblyis in the lowered position, said tape being twisted about between saidsheave means and said knee element, said tape being twisted through anadditional 90 between said sheave means and said entrance fair-lead andslots being disposed in the entrance and exit edges of said cover plateadjacent said fairleads to provide a path for said tape when said sheaveassembly is in the closed position.

20. A runway sheave assembly as set forth in claim 19. wherein saidsheave means comprises a pair of sheaves and said tape is disposedbetween said pair of sheaves.

21. A runway sheave assembly as set forth in claim I, wherein saidlocking and latching means are mounted on a pair of catch plates mountedon the walls of said pit remote from said hinge means, said lockingmeans comprising shear pin means and shear pin receiving means in saidcatch plates and on the upper portion of said cover assembly adjacentsaid plates when said assembly is in closed position and said latchmeans comprising latches mounted upon said catch plates and striker barson a lower portion of said cover assembly for engaging said latches whensaid cover assembly is in said raised position.

22. A runway sheave assembly as set forth in claim 2], wherein saidcover assembly is a truncated V-shape in plan and said catch plates aredisposed adjacent the narrower end of said V-shaped assembly remote fromsaid hinge means.

23. A runway sheave assembly as set forth in claim 1, wherein the axisof rotation of said sheave means is disposed at an oblique anglerelative to the ground when said assembly is in the raised positionwhereby the line of action of said linear payout element is inclined tothe ground to facilitate connection to an elevated cross runway element,and a substantially horizontally disposed restraining deflector isdisposed above said linear payout element between said energy absorberand said sheave means for restraining upward movement of said linearpayout element. 1

24. A runway sheave assembly as set forth in claim 23 wherein saidenergy absorber and said cross runway element are also disposed in pitsconnected to said pit for said cover assembly whereby the entireinstallation is disposed below the ground.

1. A pit-mounted runway sheave assembly for an aircraft arresting gearhaving a linear payout element connecting a cross runway element with anenergy absorber comprising a cover assembly, horizontal hinge meansconnecting said cover assembly to a side of said pit to provide raisingand closing movement thereof, a knee element mounted beneath said coverassembly remote from said hinge means and extending downwardly below it,rotatable sheave means mounted beneath said cover assembly between saidknee element and said hinge means, said knee element being long enoughto indent said linear payout element downwardly into a substantiallydeep bend into said pit, locking means which is releasable at apredetermined upward force securing said cover assembly to a wall ofsaid pit when said cover assembly is down in the closed position wherebysaid linear payout element may be pretensioned a predetermined amountwithout raising said cover assembly, said substantially deep bendcreating an upwardly directed component of force in response totensioning of said payout element which is sufficient during the initialphase of arrestment to exceed said predetermined upward force forreleasing said locking means whereby said cover assembly is allowed torise in response to the resultantly strong tensioning of said payoutelement and latching means reacting between said cover assembly and awall of said pit for holding said cover assembly in said raised positionwhereby said sheave means and said payout element are elevated aboveground level during said arrestment to facilitate their action.
 2. Arunway sheave assembly as set forth in claim 1, wherein said linearpayout element connected to each end of said runway sheave assembly isdisposed above ground level, and fairleads are disposed at the entranceand exit edges of said pit whereby said linear payout element issmoothly guided into and out of said pit.
 3. A runway sheave assembly asset forth in claim 1, wherein said cover assembly comprises a coverplate and a lower plate disposed at an acute angle relative to eachother and connected adjacent said hinge means, an inner plate disposedbetween said cover and lower plates and substantially parallel andspaced from said lower plate, said sheave means being rotatably mountedbetween said inner and said lower plates, and said knee elementextending downwardly from the edge of said inner plate remote from saidhinge means.
 4. A runway sheave assembly as set forth in claim 3,wherein the lower edge of said knee element is centrally slotted toreceive said linear payout element.
 5. A runway sheave assembly as setforth in claim 4, wherein said linear payout element comprises a lineartape disposed in contact with the lower edge of said knee element andthe side of said sheave, said lower edge of said knee element beingsubstantially horizontally disposed, and the side of said sheave meansbeing substantially vertically disposed whereby said tape is twistedabout 90* between said sheave means and said knee element.
 6. A runwaysheave assembly as set forth in claim 5, wherein said tape on both sidesof said sheave assembly is disposed aboVe the ground, entrance and exitfairleads are disposed at the entrance and exit edges of said pit forsmoothly guiding said above ground portion of said tape which aresubstantially flat with said ground when said cover assembly is in thelowered position, and said tape being twisted through an additional 90*between said sheave means and said entrance fairlead.
 7. A runway sheaveassembly as set forth in claim 1, wherein said sheave means comprises apair of sheaves and said linear payout element is disposed between saidpair of sheaves to make said sheave assembly bidirectional in action. 8.A runway sheave assembly as set forth in claim 1, wherein said lockingmeans comprises shearable means.
 9. A runway sheave assembly as setforth in claim 1, wherein said latching means comprises a resilientlatch mounted on said wall of said pit and a striker bar mounted upon alower portion of said cover assembly for engaging said resilient latch.10. A runway sheave assembly as set forth in claim 2, wherein slots areprovided through said cover assembly adjacent said entrance and exitedges of said pit to provide a path for said linear payout element tosaid sheave means and said knee element.
 11. A runway sheave assembly asset forth in claim 1, wherein a pedestal is provided in said pit to helpsupport said cover assembly within said pit in said lowered position.12. A runway sheave assembly as set forth in claim 3, whereinintermediate angular brace is disposed between said cover and said innerplate and a slotted cross brace is disposed between said inner and saidlower plates.
 13. A runway sheave assembly as set forth in claim 12,wherein said inner plate includes a pair of lateral extensions connectedbelow said cover plate.
 14. A runway sheave assembly as set forth inclaim 1, wherein said cover assembly is substantially a truncatedV-shape in plan having its narrower end disposed adjacent said runwayand said hinge means disposed at its wider end.
 15. A runway sheaveassembly as set forth in claim 14, wherein said cover assembly comprisesa cover plate and a lower plate disposed at an acute angle relative toeach other and connected adjacent said hinge means, an inner platedisposed between said cover and lower plates and substantially paralleland spaced from said lower plate, said sheave means being rotatablymounted between said inner and said lower plates, and said knee elementextending downwardly from the edge of said inner plate remote from saidhinge means.
 16. A runway sheave assembly as set forth in claim 15,wherein a pair of angular channel braces are mounted between said coverand said inner plates and substantially parallel to the sides of saidtruncated V-shaped cover assembly.
 17. A runway sheave assembly as setforth in claim 16, wherein a cross brace comprising a centrally slottedchannel is laterally secured between said inner and said lower plates,and said central slot providing a path for said linear payout elementthrough said cover assembly.
 18. A runway sheave assembly as set forthin claim 17, wherein the lower edge of said knee element is slotted toprovide a path for said linear payout element.
 19. A runway sheaveassembly as set forth in claim 18, wherein said tape on both sides ofsaid sheave assembly is disposed above the ground, entrance and exitfairleads are disposed at the entrance and exit edges of said pit forsmoothly guiding said above-ground portions of said tape which aresubstantially flat with said ground when said cover assembly is in thelowered position, said tape being twisted about 90* between said sheavemeans and said knee element, said tape being twisted through anadditional 90* between said sheave means and said entrance fair-lead,and slots being disposed in the entrance and exit edges of said coverplate adjacent said fairleads to provide a path for said tape when saidsheave assembly is in the closed position.
 20. A runway sheave assemblyas set forTh in claim 19, wherein said sheave means comprises a pair ofsheaves and said tape is disposed between said pair of sheaves.
 21. Arunway sheave assembly as set forth in claim 1, wherein said locking andlatching means are mounted on a pair of catch plates mounted on thewalls of said pit remote from said hinge means, said locking meanscomprising shear pin means and shear pin receiving means in said catchplates and on the upper portion of said cover assembly adjacent saidplates when said assembly is in closed position and said latch meanscomprising latches mounted upon said catch plates and striker bars on alower portion of said cover assembly for engaging said latches when saidcover assembly is in said raised position.
 22. A runway sheave assemblyas set forth in claim 21, wherein said cover assembly is a truncatedV-shape in plan and said catch plates are disposed adjacent the narrowerend of said V-shaped assembly remote from said hinge means.
 23. A runwaysheave assembly as set forth in claim 1, wherein the axis of rotation ofsaid sheave means is disposed at an oblique angle relative to the groundwhen said assembly is in the raised position whereby the line of actionof said linear payout element is inclined to the ground to facilitateconnection to an elevated cross runway element, and a substantiallyhorizontally disposed restraining deflector is disposed above saidlinear payout element between said energy absorber and said sheave meansfor restraining upward movement of said linear payout element.
 24. Arunway sheave assembly as set forth in claim 23 wherein said energyabsorber and said cross runway element are also disposed in pitsconnected to said pit for said cover assembly whereby the entireinstallation is disposed below the ground.